Electro-hydraulic shock wave systems are used to generate pressure pulses by applying voltage by means of an RLC discharge circuit between two electrodes located in a fluid, causing a plasma to form between the electrodes during the discharge, generating a shock wave.
The properties of the shock wave depend significantly on the discharge current and the charging voltage. These, in turn, result from the parameters of the RLC circuit, the applied voltage and the geometry of the electrode configuration.
Document DE 40 20 770 elucidates the characteristic of the discharge curves of current and voltage, Conventional systems make use of a damped oscillation.
The breakdown of the discharge voltage between the tips of the electrodes, which usually are located in an aqueous solution, is a statistical effect, since local physical conditions of the electrical field and the inhomogeneities of the medium located between the tips cause extreme variations in the formation of the electric arc and of the plasma. The reproducibility of the discharge is made more difficult by the fact that the electrode tips wear out after many discharges, which not only alters the surface roughness, but also increases the distance between the electrodes due to loss of material in the tips. In the course of time, this results in an increase in the minimum voltage, which is necessary in order to achieve a breakdown.
From DE 40 20 770 it is known that this problem can be countered by using a highly conductive electrolyte as the fluid in which the electrodes are located. The discharge then becomes a type that is critically damped, in which the latency time, i.e. the time until the breakdown, is more or less completely suppressed, since the electrical energy is converted directly to form a vapor bubble and therefore a pressure wave, so that the formation of a plasma does not even come about.
However, this apparatus requires a very careful control of the electrode distance, since the system reacts very sensitively to this distance.
Another procedure is depicted in EP 0911 804. This document describes an apparatus that measures the directly controlled distance, i.e. voltage and its gradient, and varies the distance between the electrodes based on deviation from a set voltage. The set value is defined so that when it is reached the optimum conversion of electrical energy into pressure energy takes place. The increase in distance between the electrode tips can therefore be corrected, increasing the life of the electrodes. The individual shock waves are more similar to each other, because they are generated at least with equivalent electrode geometry. Depending on whether a constant or a variable reference value is used, the electrode distance can be increased or decreased.
However, voltage measurement in a high-voltage discharge circuit is difficult to implement. Interference causes very high proneness to errors.
The object of the invention is to present an apparatus and a process for optimized electro-hydraulic pressure pulse generation that records characteristic parameters which can be measured insusceptible to error and compared with set values. A voltage measurement alone furthermore enables no conclusion about the energy conversion between the electrodes.
The object of the invention is achieved by an apparatus in which an electro-hydraulic shock wave system is provided with a measuring and control device that measures the discharge current between the electrode tips, and a process that influences the system parameters by means of the apparatus.